1. Field of the Invention
The present invention relates to a method and an apparatus for pre-processing stainless steel intended to be cold-rolled, and capable of advantageously manufacturing cold-rolled stainless steel strip exhibiting an excellent surface luster.
More specifically, the present invention relates to an improvement in a method of pre-processing a hot coil made of stainless steel prior to cold rolling, and, more particularly, to an improvement in the A.P. (Annealing and Pickling) line.
2. Description of the Background Art
Cold-rolled stainless steel strip has been manufactured by pickling hot rolled-stainless steel strip after annealing; cold rolling the hot-rolled stainless steel strip with the surface which has been pickled remaining as it is; annealing and pickling the cold-rolled stainless steel or bright-annealing the same; and temper rolling at a reduction ratio of 1.2% or less.
Since ferritic stainless steel strips represented by JIS SUS430 are usually used without additional processing after temper rolling, a satisfactory surface luster is required. On the other hand, austenitic stainless steel strips represented by JIS SUS304 are usually subjected to buffing after temper rolling in order to obtain an excellent surface luster.
Therefore, processing to keep the surface roughness low is necessary for both ferritic and austenitic stainless steel strips when the temper rolling has been completed. In the case where the cold rolling is conducted by using a small-diameter work roll such as a Sendzimir mill, a method in which the roughness of the work roll is reduced has been disclosed in, for example, Japanese Patent Publication No. 57-13362. However with such a method, the luster of the surface of the final product is insufficient since excessive roughness, which is observed on the surface of the steel strip after hot rolling, remains even after completion of cold rolling.
On the other hand, a tandem mill rolling method using a large diameter work roll having a diameter larger than 150 mm.phi. has been employed, with which cold-rolled stainless steel strips can be efficiently manufactured by considerably shortening the rolling time. Also according to this method, similarly to the above-described method in which the Sendzimir mill is used, excessive roughness remains on the surface of the hot rolled steel strip after annealing, even after cold rolling. What is worse, the degree of roughness becomes excessive in comparison to the degree of roughness caused by rolling with the Sendzimir mill. Therefore, the products thus manufactured cannot be used when luster of surface is required.
In order to overcome the problems referred to above, a method has been disclosed in which the diameters of the work rolls are combined so as to realize the desired effect. This has been disclosed in, for example, Japanese Patent Laid-Open No 61-49701. Also according to this method, as in Japanese Patent Publication No. 57-13362, excessive roughness remains on the surface of steel strip which has been annealed and pickled after hot rolling and after cold rolling.